The invention described herein relates to orthodontic appliances and their use is the practice of orthodontics. More specifically, it relates to coiled wire springs which may easily be prefabricated and which are rapidly and easily installed in the mounth to correct malocclusions of teeth. In orthodontics it is frequently necessary to move teeth along the jaw so as to assure proper spacing and correct malocclusions. This movement is termed retraction. Retraction of individual teeth in orthodontic treatment is accomplished by various mechanisms and techniques. The ideal retraction mechanism would be one that applies a force no greater than the capillary pressure of the peridontal membrane. No practical force mechanism is available that creates a constant force of this minute magnitude. However, it is generally accepted that the bodily retraction of a tooth without severe loss of anchorage is best accomplished with light forces.
The design of fixed orthodontic appliances and the oral environment combine to restrict the retraction mechanisms to a limited number of forms or techniques. One important restriction is the distance over which the activated retraction mechanism can provide the requisite retraction force. Ideally, a single activation would retract an individual tooth the total required distance with a continuous light force. In actual practice it has heretofore been difficult to apply the necessary force in anything approaching a constant manner. Other important considerations in the design of retraction mechanisms are the ease of placement and removal and the ability to withstand the forces of mastication without breakage or deformation. An additional consideration is the desirability of eliminating patient responsibility for activation or placement of the mechanism. Finally, it should be an intra-oral device.
Prior art intra-oral retraction mechanisms include closed coil metallic springs, open coil metallic springs, and elastic materials. Elastic bands of certain rubbers or plastics have several advantages insofar as they can be inserted and removed by the patient, do not have to be cleaned because they are disposable, and do not have to be reactivated by the orthodontist. Unfortunately, they also have a number of rather severe disadvantages. The fact that they can easily be removed by the patient at will serves to frustrate the orthodontist's efforts if they are in fact prematurely removed. More importantly, presently used elastic materials are subject to interaction with the natural fluids in a patient's mouth. This interaction rapidly degrades the physical properties of the conventional strand elastics, resulting in a tensile force reduction of about 40% after the elastics have been in place for only a few hours. Accordingly, the restoring force exerted by the elastic when stretched to a specific elongation does not remain constant and is difficult to control. For this reason, elastic bands require freqent replacement.
Closed coil springs of metal wire are used as retraction mechanisms by attaching them in tension between a fixed anchor point in the mouth and the tooth desired to be moved. The tension expands or opens the coils of the spring and the retractive force is produced by the coils attempting to close to the rest position. It will be apparent that as the retracting tooth moves, the coils approach nearer to the rest position and, as a result, the force acting on the tooth is reduced.
Open coil springs operate just the reverse of closed coil springs. In operation, they are placed in compression so that the coils supply a retractive force by attempting to move back to the open, rest position. As a practical matter, open coil springs are not as frequently used for retraction although some orthodontists do use them for this purpose.
The standard closed coil retracting springs have straight wires at either end which are used to mount them to brackets on an anchor tooth and the tooth to be retracted. Tying these ends to the brackets is often a difficult procedure, especially in the back of the mouth. Frequently, it is time consuming. Removal is also time consuming, requiring in the usual practice that the spring coils be cut and the ends then unwrapped from the brackets on the teeth. In the back of the mouth this unwrapping may inadvertently result in puncture wounds in the cheek or gum because the wire is normally of small diameter and readily penetrates tissue. In any case, the process is normally uncomfortable to the patient.
It will be apparent that it is highly desirable to minimize or avoid tying or wrapping procedures altogther--particularly in the back of the mouth--while at the same time assuring that the retracting spring is not capable of being readily removed by the patient.
In U.S. Pat. No. 3,936,938 for "Orthodontic Spring Appliance and Spring Clip Therefor" issued on Feb. 10, 1976, the inventor discloses apparatus for avoiding the wrapping problem. In this apparatus, at least one end of the retraction spring has a straight extension having protrusions thereon spaced at predetermined intervals. The wire with protrusions may readily be connected to a spring clip which may be attached to the arch wire or a tooth bracket. The clip has a slot therein which is so designed that it readily accommodates the protrusion but prevents the wire from being pulled out by the tension force of the spring. It should be noted that the spring appliance of U.S. Pat. No. 3,936,938 requires the use of a special spring clip which appears to have no utility other than as an anchor point for the retraction spring. Further, spring clips of the type disclosed in this patent are subject to occasional inadvertent release of the spring. They also permit the patient to easily release the spring. In either instance, the purpose of the orthodontist is nullified.